The present invention relates to a system for transmitting a digital video signal and recording the received video signal. More particularly, the present invention relates to great extension of the range of use of a digital signal recording/reproducing system by greatly shortening a recording time through transmission of a video signal in a compressed form, and further relates to great extension of the range of use of a digital signal recording/reproducing system by making the number of signals to be recorded and a recording/reproducing time variable.
As a digital magnetic recording/reproducing system (hereinafter referred to as VTR) is conventionally known, for example, a D2 format VTR. In such a conventional digital VTR, the elongation or shortening of a reproducing time is possible by using variable-speed reproduction. However, the prior art reference does not at all disclose high-speed recording in which a recording time is shortened to 1/m, multiple recording in which a plurality of signals are recorded, and the compression/expansion of a recording/reproducing time.
The above-mentioned conventional digital VTR has a feature that a high quality is attained and there is no deterioration caused by dubbing. However, the shortening of a dubbing time is not taken into consideration. Therefore, for example, in the case where a two-hour program is to be recorded, two hours are required. Thus, there is a drawback that inconveniences are encountered in use. Also, the multiplexing of recording signals is not taken into consideration. Therefore, for example, when two kinds of programs are to be simultaneously recorded or reproduced, two VTR""s are required. This also causes inconveniences in use.
An object of the present invention is to provide a digital VTR in which high-speed recording onto a tape can be made with the same format as that used in standard-speed recording, to provide a transmission signal processing system for transmitting at a high speed a video signal to be recorded by such a digital VTR, and to extend the range of use of the digital VTR by shortening a recording time. For example, the digital VTR can be used in such a manner that a two-hour program is recorded in about ten minutes and is reproduced at a standard speed.
The above object is achieved as follows. A video signal and an audio signal are subjected to time-base compression to 1/m, bit compression to 1/n, addition of a parity signal and modulation, and are thereafter transmitted or outputted. The transmitted signal is received, is subjected to demodulation, error correction, addition of a parity signal and modulation, and is thereafter recorded, onto a magnetic tape which travels at a travel speed m times as high as that upon normal reproduction, by use of a magnetic head on a cylinder which rotates at a frequency m times as high as that upon normal reproduction. The signal on the magnetic tape traveling at a travel speed upon normal reproduction is reproduced by a magnetic head on the cylinder which rotates at a frequency upon normal reproduction. The reproduced signal is subjected to demodulation, error correction, bit expansion of video and audio signals and D/A conversion, and is thereafter outputted. Address signals corresponding to a plurality of VTR""s may be transmitted prior to a signal to be recorded. Further, control signals indicative of the start of recording and the stop of recording may be transmitted. The transmitted signals are received and error-corrected, and controls of the standby for recording, the start of recording and the stop of recording are made on the basis of the control signals.
With the above construction, since the video signal and the audio signal are time-base compressed to 1/m and bit-compressed to 1/n, a transmission time is shortened to 1/m and a signal band turns to m/n. The time-base compressed and bit-compressed signal is transmitted after addition of a parity signal for error correction and modulation to a code adapted for a transmission path. The transmitted signal is received and demodulated. The detection of an error produced in a transmitting system and the correction for the error can be made using the added parity signal. The error-corrected signal is added with a parity signal for correction for an error produced in a magnetic recording/reproducing system and is modulated to a code adapted for the magnetic recording/reproducing system. Upon recording, since the rotation frequency of the cylinder and the travel speed of the magnetic tape are increased by m times, the recording onto the magnetic tape can be made at an m-tuple speed. Upon reproduction, by setting the rotation frequency of the cylinder and the travel speed of the magnetic tape to normal ones, the reproduction at a normal speed can be made. The reproduced signal is code-demodulated. The detection of an error produced in the magnetic recording/reproducing system and the correction for the error can be made on the basis of the parity signal. By bit-expanding the video signal and the audio signal compressed by the transmission signal processing system, the original video and audio signal can be restored. The bit-expanded signal is converted into an analog signal by a D/A converter. Simultaneous and selective control of the start/stop of recording for a multiplicity of VTR""s can be made in such a manner that the address signals corresponding to the VTR""s are transmitted prior to a signal to be recorded, the correction for an error of the received signal is made, required VTR""s are brought into recording standby conditions by the corrected address signals, and the controls of the start of recording and the stop of recording are made by the transmitted control signals.
Another object of the present invention is to provide a digital signal recording/reproducing system in which multiple recording onto a tape can be made with the same format as that used in standard recording and simultaneous multiple reproduction is possible, and to extend the range of use of a digital VTR by compressing/expanding a recording/reproducing time in accordance with the transmission rate of a multiplexed input/output signal and the number of signals in the multiplexed input/output signal.
This object is achieved as follows. There are provided means for selecting one or plural desired signals from a time-base compressed and time-division multiplexed digital input signal, and helical scan recording means for making time-division multiplex recording of the selected signals with a time-base compressed speed after selection being retained. There is further provided means for reproducing the recorded signals with the rotation speed of a cylinder, a tape speed and so on being set to values proportional to the transmission rate of a reproduction signal and the number of signals to be simultaneously reproduced and with the signal being time-base expanded or being retained as time-base compressed.
With the above construction, N kinds of desired signals selected from the multiplexed input digital signal and time-base compressed to 1/K are subjected to time-division multiplex recording with a time-base compressed speed after selection being retained. Upon reproduction, for example, if both the cylinder rotation speed and the tape speed are set to N/K times, a recording track and a reproducing track coincide with each other and the use of a reproducing time K/N times as long as a recording time enables the reproduction of each of the N kinds of signals at a standard speed. Also, if both the cylinder rotation speed and the tape speed are set to (Mxc3x97N)/K times, a recording track and a reproducing track coincide with each other and the use of a reproducing time as K/(Mxc3x97N) times as long as the recording time enables the reproduction of each of the N kinds of signals at an M-tuple speed. In the case where L kinds of signals are selected from among the N kinds of reproduced signals and a processing speed at a reproduction signal processing circuit is set to Lxc3x97M times as long as a standard reproduction processing speed, each of the L kinds of signals among the N kinds of multiple-recorded signals is outputted at a speed M times as high as a standard speed.